In various industrial, chemical, metallurgical and heating processes, waste heat carrying fluids at a temperature of above 150.degree. C. can be effectively subjected to waste heat recovery, e.g. in so-called waste heat boilers, to produce low pressure steam. The steam can be used as process steam for a variety of purposes and as a heat-exchange fluid for plant heating and other purposes.
However, when a fluid is obtained at a lower temperature level as a carrier of the waste heat, the waste heat has not been effectively recovered in most instances and because this small amount of thermal energy is not readily recoverable, e.g. because there are few consumers of such low temperature heat, the waste heat is discharged and represents an energy loss.
Experience has shown that direct use of fluids at temperatures below 150.degree. C. as heating sources is difficult and seldom practical.
Obviously the low temperature fluids which still contain significant sensible heat can represent a valuable energy source if this heat can be recovered in a practical manner and in a readily usable fashion.